1. Field of the Invention
Aspects of this invention relate generally to mold inserts, and more particularly to an undercut mold insert capable of selectively and sufficiently flexing or otherwise mechanically shifting for use in forming groove-like undercuts on an inner surface of a molded part.
2. Description of Related Art
By way of background, a major concern in the molding industry is how to successfully and consistently form a groove in at least a portion of an inner surface of a molded part. One type of molded part that requires such a groove are frames for holding lenses, such as in eyewear; the groove being configured for holding a lens therewithin. Presently, manufacturers typically use a rigid steel or other metal “potato chip” insert. With the insert located within an injection mold, the mold is closed about the insert, and the plastic material is injected into the mold. The insert extends into the cavity of the mold to form the lens retention groove. Upon cooling, the insert is pulled or pushed out. Because the insert is relatively rigid compared to the frame material, and because the frame material tends to be at its most fragile state right after cooling, the lip of the retention groove, along with the rest of the frame, has a tendency to become deformed while being pulled or to snap back and create surface marring and stress fractures that are unacceptable under industry standards. This not only produces a high “scrap rate” (often up to twenty-five percent or more due to unacceptable permanent deformation of the frame), but it also limits frame design options to essentially only those that can accommodate the removal of such a rigid insert during the molding process. Further, rigid inserts tend to damage the mold itself and drive up tooling and repair costs, causing some manufacturers to resort to manually removing the molded part from the mold. Finally, manufacturers using rigid inserts are limited to relatively shallow retention grooves, because deeper grooves would not permit withdrawal of rigid inserts without damage and, thus, even higher scrap rates.
In an attempt to solve these problems, some manufacturers use relatively flexible mold inserts, as opposed to the traditional rigid inserts. Because these improved inserts are able to flex as they are pulled from the molded groove, the likelihood of the groove being deformed or the frame damaged is reduced. However, even these flexible inserts must still have a certain degree of rigidity so as to maintain their structural integrity during the molding process and ensure that the groove is properly formed about the inner surface of the molded part. Thus, while these flexible inserts may reduce the scrap rate, they can still cause the same deformation and surface marring as the more rigid inserts, especially when the groove being formed is relatively deep.
A still further improved insert, as described in U.S. Pat. No. 3,406,232 to Barker, comprises a resilient ring-like structure that is used in the molding of undercuts in substantially the same way as the above described rigid and flexible “potato chip” inserts. This improved insert provides a pair of tool-receiving holes positioned proximal diametrically opposed edges thereof. Thus, upon cooling of the molded frame, a special tool is inserted into each of the tool-receiving holes, enabling the tool to pinch and radially deform the insert such that the diametrically opposed edges proximal the holes become at least partially disengaged from the undercut, which allows the insert to then be more easily removed from the frame. While such an insert design allows for relatively easier removal from the frame, as compared to the “potato chip” prior art, the fact that at least a portion of the insert edge remains in contact with the undercut after the insert has been radially deformed means that there will still potentially be a certain amount of resistance in removing the insert. Thus, depending on the materials of construction used in each of the insert and molded frame, as well as the size and shape of the frame and associated undercut being formed, there is still a chance that removal of such an insert will cause similar deformation and surface marring as the “potato chip” inserts.
Therefore, there is still a need for a mold insert capable of selectively and sufficiently flexing or otherwise mechanically shifting such that substantially the entire perimeter edge of the insert may be disengaged from within the frame undercut before the insert is removed, thus enabling the insert to produce relatively deep retention grooves to effectively hold lenses even in complex frame designs, while substantially reducing both scrap rates and tooling costs. Aspects of the present invention fulfill these needs and provide further related advantages as described in the following summary.